[media] uvcvideo: Move fields from uvc_buffer::buf to uvc_buffer

Add mem, length and bytesused fields to the uvc_buffer structure and use
them instead of accessing the uvc_buffer::buf m.offset, length and
bytesused fields directly. This prepares the driver to the conversion to
videobuf2.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/drivers/media/video/uvc/uvc_isight.c b/drivers/media/video/uvc/uvc_isight.c
index 74bbe8f..8510e725 100644
--- a/drivers/media/video/uvc/uvc_isight.c
+++ b/drivers/media/video/uvc/uvc_isight.c
@@ -74,7 +74,7 @@
 	 * Empty buffers (bytesused == 0) don't trigger end of frame detection
 	 * as it doesn't make sense to return an empty buffer.
 	 */
-	if (is_header && buf->buf.bytesused != 0) {
+	if (is_header && buf->bytesused != 0) {
 		buf->state = UVC_BUF_STATE_DONE;
 		return -EAGAIN;
 	}
@@ -83,13 +83,13 @@
 	 * contain no data.
 	 */
 	if (!is_header) {
-		maxlen = buf->buf.length - buf->buf.bytesused;
-		mem = queue->mem + buf->buf.m.offset + buf->buf.bytesused;
+		maxlen = buf->length - buf->bytesused;
+		mem = buf->mem + buf->bytesused;
 		nbytes = min(len, maxlen);
 		memcpy(mem, data, nbytes);
-		buf->buf.bytesused += nbytes;
+		buf->bytesused += nbytes;
 
-		if (len > maxlen || buf->buf.bytesused == buf->buf.length) {
+		if (len > maxlen || buf->bytesused == buf->length) {
 			uvc_trace(UVC_TRACE_FRAME, "Frame complete "
 				  "(overflow).\n");
 			buf->state = UVC_BUF_STATE_DONE;